The present invention relates, in general, to electronics and, more particularly, to a brushless DC motor.
Brushless Direct Current (DC) motors are used in a variety of applications including disc drives, compact disc players, digital video disc players, scanners, printers, plotters, actuators used in the automotive and aviation industries, etc. Typically, multiple phase motors include a stationary portion or stator that produces a rotating magnetic field and a non-stationary portion or rotor in which torque is created by the rotating magnetic field. The torque causes the rotor to rotate which in turn causes a shaft connected to the rotor to rotate. At start-up it is desirable to detect the position and rotation rate of the brushless DC motor's rotor. In a brushless DC motor having sensors, the rotor position and its rotation rate may be detected and controlled using Hall sensors. However, the accuracy of Hall sensors is influenced by their operating environment, which decreases the accuracy of the measurements they provide. In sensorless brushless DC motors, the position of the rotor is detected using a Back ElectroMotive Force (BEMF) signal. A drawback with using a BEMF signal is that the BEMF is typically compared with a voltage generated by a high voltage PNP circuit element, which is not suitable for miniaturization using monolithic integrated circuit processes. Another drawback is that the comparator is limited to comparing positive voltages. Another drawback with using a BEMF signal is that it becomes very small when the rotor is moving slowly or not at all.
Accordingly, it would be advantageous to have a method and structure for detecting a rotor position that accommodates a high input voltage range and has a high noise immunity. It is desirable for the method and structure to be cost and time efficient to implement.
For simplicity and clarity of illustration, elements in the figures are not necessarily to scale, and the same reference characters in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or an anode of a diode, and a control electrode means an element of the device that controls current flow through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain n-channel or p-channel devices, or certain n-type or p-type doped regions, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with embodiments of the present invention. It should be noted that a doped region may be referred to as a dopant region. It will be appreciated by those skilled in the art that the words during, while, and when as used herein are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay, such as a propagation delay, between the reaction that is initiated by the initial action and the initial action. The use of the words approximately, about, or substantially means that a value of an element has a parameter that is expected to be very close to a stated value or position. However, as is well known in the art there are always minor variances that prevent the values or positions from being exactly as stated. It is well established in the art that variances of up to about ten percent (10%) (and up to twenty percent (20%) for semiconductor doping concentrations) are regarded as reasonable variances from the ideal goal of being exactly as described.